Choosing the right battery for nRF51?

[Texton]

Hi all,

BACKGROUND:

I'm working on a project where we use the nRF51, and our first prototype boards just arrived.

So I've made some power measurements trying to calculate the battery life:

When idle: 3,1uA
When bluetooth connected: 4,5mA

The bluetooth won't be connected that often, so this I can actually live with the resulting battery life for the prototype (gives me around 17-18 weeks battery life).

We're using a Panasonic CR1216 battery: industrial.panasonic.com/.../AAA4000C277.pdf

And just now I realised that the battery voltage takes a good drop when the bluetooth is connected for a longer time. The max connected time is 10sec and there I got:

Start: 2,99V drops exponentially to 2,7V over 10sec. 

When the bluetooth disconnects it slowly climbs towards 2,99V again. I've waited 10min now and it is around 2,96V.

QUESTION:

In the battery datasheet I can't find anything about max discharge current? But clearly the 4,5mA is too much, and I found a similar battery (www.rossmannweb.de/.../CR1216_Renata_Rossmann.pdf ) where max discharge current is 1mA. So question is what will happen to the battery's 25mAh? (in general terms). And do you think it will be worth to look for an other battery that can handle higher discharge currents? - in that case any suggestions?

[Dave_couling]

Also look into your peak current pulses. a CR2016 can only handle 5-8mA peaks. So be sure to measure your Tx and Rx peaks

[Øyvind Karlsen]

Hi,

Your estimate for bluetooth connected seems a bit high compared to the online power profiler for nRF52(even though you are using 51 this is an OK guidance, just add a multiplier of 1.5-2).

We have had success with CR2032 (15 mA pulsed discharge, 3 mA continous) and similar batteries. From working with other batteries you will experience voltage drops when working with heavy loads, generally you will get shorter battery lifespan, this is sometimes seen in a curve plot with current vs operating hours in datasheets.

Best regards,

Øyvind